Von benten



March 1o, 1964 H. VON BENTEN 3,124,109

ONCE-THROUGH STEAM GENERATOR Filed sept. 50. 1960 Y L 2e so 3o l l I fao 10/v "22 "1o" *To* 22- f`1o r l "1 "-l l--l '-m 30 30 2af-L. L L L u L 2e 3o l -1 --I r| -1 l r`3o f2o 2o- 32 32 1 24 4 L I 12 l 6 34 i 1 r INVENToR.

Hans 'von Benren BY 6` ATTORNEY United States Patent() 3,124,109 ONCE-THROUGH STEAM GENERATOR Hans von Eenten, Ratingen, Germany, asslgnor to Durr- Werke Aktiengesellschaft, Ratingen, Germany, a corporation of Germany Filed Sept. 30, 1960, Ser. No. 59,752 1 Claim. (Cl. 122-406) This invention relates in general to forced llow fluid heating units and more particularly to improvements in the construction and operation of lluid heating circuits adapted for use in a forced circulation once-through vapor generating and superheating unit.

The construction of forced circulation high pressure steam generators requires the use of a large number of parallel llow circuits connected between inlet and outlet headers. kOne of the fundamental problems involved in the design of such a steam generator is the control of the llow through the various parallel circuits in order that the llow in each circuit will be stable and the enthalpy of the fluid discharged from any individual circuit will be close to the average of that from all circuits, in which case the circuits will be in a balanced flow condition. When steam or water, or mixtures thereof, is heated in parallel llow paths provided by, for example, the furnace wall tubes or tubular panels disposed in the furnace, unbalanced lluid ilow distribution may lead to excessive localized tube metal temperatures and/or to excessive temperature differentials between adjacent furnace wall tubes and, thereby, to undue thermal stresses in the furnace wall-forming components. lf the llow of the working medium or lluid through the individual tubes of the parallel lloW circuits is to be properly balanced, care must be taken that the lluid pressure drop between the inlet and outlet headers, due largely to friction, is sufficiently high. But since the friction loss is proportionate to the square of the rate of lluid llow, partial load operation presents the danger that the pressure drop necessary for adequate and balanced fluid llow distribution will not be attained.

To overcome the problem of unbalanced lluid llow distribution in a steam generator of the character described, attempts have been made to provide for an adequate pressure drop at partial loads by keeping the velocity of llow appropriately high or by installing llow restrictors of a fixed size in the tubes of the parallel llow circuits. These restrictors impose a resistance to fluid flow which has a proportioning and equalizing effect on the amount of fluid entering each tube.

While selection of an appropriate high velocity of lloW oders the advantage of adequate cooling of the 3,124,109 Patented Mar. 10, 1964 ICC system is provided with a multiplicity of lluid heating circuits arranged for parallel llow of lluid therethrough and connected into the circulation system, with the cir cuits supplied with fluid from a common source. Automatically adjustable throttling members are provided in each of the parallel ilow circuits and are responsive to variations in the rate of fluid flow for maintaining the pressure drop of the lluid in flowing through the circuits substantially constant throughout the load range, thereby effecting balanced distribution of iluid from the common source to the circuits. This arrangement makes it possible to operate the steam generator at part loads'y as low as 301% of normal load in a simple and dependable manner, with balanced distribution of lluid to all circuits being assured and the lluid pressure drop necessary for balanced distribution being automatically maintained at the proper level.

The various features of novelty which characterize my invention are pointed out with particularity in the claim annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference tubes throughout the load range, it entails the drawback of a very high pressure loss in the upper portion of the load range, which means increased auxiliary power by reason of the work done by the feed pump. Although this disadvantage can be compensated in some measure by alternatively installing flow restrictors, nevertheless a substantial pressure drop will occur with increasing rate of lluid flow.

It has further been proposed to make the headers of the parallel llow circuits relatively short so that each header `supplies but a few parallel flow tubes. While this construction results in considerable improvement in the distribution of the working medium to the tubes, the circuits are very susceptible to unstable llow, under which condition more than one llow can occur for the same pressure drop.

The present invention solves the problem of unbalanced llow and overcomes the drawbacks of prior constructions. In accordance with the invention a steam generator having a forced circulation fluid circulation should be had to the accompanying drawing and descriptive matter in which I have illustrated and described a preferred embodiment of the invention.

The accompanying drawing is a schematic representation of lluid heating cir-cuits constructed and operable in accordance with the invention and particularly adapted for use in a forced circulation once-through steam generator. According to the invention, a steam generator of the character described comprises a multiplicity of fluid heating circuits 10 arranged for parallel flow of lluid therethrough relative to each other and normally subject to the heat of high temperature gases. The parallel ilow circuits 10 have their supply and discharge ends respectively connected to common inlet and outlet headers 12 and 14, with a conduit 16 connected to the header 12 for Supply of iluid thereto from a common source by means of a feed pump, not shown, and with the header 14 being arranged for discharge of lluid to an outlet conduit 18, which passes the iluid to other heating circuits, not shown, of the steam generator. -Each circuit 10 comprises three tube panels 20 serially connected with one another by tubes 22 and with the headers 12 and 14 by tubes 24 and 26, respectively, with each tube panel comprising a group of laterally spaced tubes arranged in parallel llow relation and extending between common inlet and outlet headers 28 and 30, respectively, of relatively short length. Each circuit 10 also includes a valve 32, or other suitable throttling member, disposed in the tube 24. Tube 16 is provided with an impulse generator or controller 34 which automatically and continuously measures the value of the rate of fluid lloW to the parallel llow circuits, and translates any deviation from some pre-set value of rate of fluid low into an impulse force change, which is transmitted to the valves 32 by way of line 36 to move all of the valves simultaneously, thereby automatically regulating the lluid pressure drop across the valves 32 in accordance with the demand on the steam generator. Alternatively, the valves 32 may be disposed between the tube panels or downstream lllow-Wise of the last tube panel of each circuit. Each valve 32 is preset so that it is at its maximum open position at full load and at its minimum open position at a predetermined partial load.

In operation, iluid is supplied to the header 12 by way of the conduit 16, then passes in parallel llow relation through the tubes 24 and valves 32 to the tube panels 20, with the lluid stream of each circuit then passing serially to the header 14 by way of the tube panels 20, while subdividing into a multiplicity of parallel llow streams and then combining into a single stream as it passes into and out of each tube panel 20. At full load each of the valves 32 is at its maximum open position since the velocity of flow at this load is high enough to provide a pressure differential between the inlet header 12 and the outlet header 14 suicient to assure balanced distribution of fluid to the parallel flow circuits. As the load decreases, the impulse generator 34 automatically transmits an impulse by Way of the line 36 to simultaneously move the valves 32 toward their minimum open positions to the extent that the -fluid pressure drop between the headers 12 and 14 is maintained substantially constant from full load to some predetermined partial load, preferably one-third load, which assures balanced distribution of fluid to the tubes of the panels 20 throughout this load range.

While in accordance With the provisions of the statutes I have illustrated and described herein the best form and mode of operation of the invention now known to me those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by my claim, and that certain features of my invention may sometimes be used to advantage Without a corresponding use of other features.

What is claimed is:

In a steam generator having a forced circulation fluid circulation system, a plurality of Huid heating circuits arranged for parallel ow of `fluid therethrough and connected into said circulation system and subject to the heat of high temperature gases, a common source of vaporizable iluid, means for supplying the fluid in parallel 'flow relation from said common source to said circuits, and means `for maintaining the pressure drop of the uid due to flow through said circuits substantially constant from full load to a predetermined partial load to effect balanced distribution of the Huid from the common source to said circuits, said last named means including a valve member in each of said circuits, means interconnecting all of said valve members, and means responsive only to variations in total rate of fluid ow to said circuits for simultaneously moving the valves in a closing direction as the rate of Huid llow to said circuits decreases.

References Cited in the le of this patent UNITED STATES PATENTS 2,098,913 Dickey Nov. 9, 1937 2,170,347 Dickey Aug. 22, 1939 2,626,627 Jung Jan. 27, 1953 2,805,653 Junkins Sept. 10, 1957 2,985,151 Dickey May 23, 1961 FOREIGN PATENTS 300,656 Great Britain Nov. 28, 1929 384,832 Great Britain Dec. 15, 1932 779,335 Great Britain July 17, 1957 1,001,284 Germany Jan. 24, 1957 

